Advances in cell-replacement therapy for Type I diabetes mellitus and a shortage of transplantable islets of Langerhans have focused interest on developing sources of insulin-producing cells, or β cells, appropriate for engraftment. One approach is the generation of functional β cells from pluripotent cells, such as, for example, embryonic stem cells.
In vertebrate embryonic development, a pluripotent cell gives rise to a group of cells comprising three germ layers (ectoderm, mesoderm, and endoderm) in a process known as gastrulation. Tissues such as, for example, thyroid, thymus, pancreas, gut, and liver, will develop from the endoderm, via an intermediate stage. The intermediate stage in this process is the formation of definitive endoderm. Definitive endoderm cells express a number of markers, such as, HNF-3 beta, GATA-4, Mix11, CXCR4 and SOX-17.
Formation of the pancreas arises from the differentiation of definitive endoderm into pancreatic endoderm. Cells of the pancreatic endoderm express the pancreatic-duodenal homeobox gene, PDX-1. In the absence of PDX-1, the pancreas fails to develop beyond the formation of ventral and dorsal buds. Thus, PDX-1 expression marks a critical step in pancreatic organogenesis. The mature pancreas contains, among other cell types, exocrine tissue and endocrine tissue. Exocrine and endocrine tissues arise from the differentiation of pancreatic endoderm.
The generation of a sufficient amount of cellular material for transplantation requires a source of the cellular material that can be efficiently expanded in culture, and efficiently differentiated into the tissue of interest, for example, functional β cells.
Current methods to culture human embryonic stem cells are complex; they require the use of exogenous factors, or chemically defined media in order for the cells to proliferate without loosing their pluripotency. Furthermore differentiation of embryonic stem cells often results in a decrease in the cells to expand in culture.
In one example, Cheon et al (BioReprod DOI:10.1095/biolreprod.105.046870, Oct. 19, 2005) disclose a feeder-free, serum-free culture system in which embryonic stem cells are maintained in unconditioned serum replacement (SR) medium supplemented with different growth factors capable of triggering embryonic stem cell self-renewal.
In another example, US20050233446 discloses a defined media useful in culturing stem cells, including undifferentiated primate primordial stem cells. In solution, the media is substantially isotonic as compared to the stem cells being cultured. In a given culture, the particular medium comprises a base medium and an amount of each of bFGF, insulin, and ascorbic acid necessary to support substantially undifferentiated growth of the primordial stem cells.
In another example, WO2005086845 discloses a method for maintenance of an undifferentiated stem cell, said method comprising exposing a stem cell to a member of the transforming growth factor-beta (TGFβ) family of proteins, a member of the fibroblast growth factor (FGF) family of proteins, or nicotinamide (NIC) in an amount sufficient to maintain the cell in an undifferentiated state for a sufficient amount of time to achieve a desired result.
Inhibitors of glycogen synthase kinase-3 (GSK-3) are known to promote proliferation and expansion of adult stem cells. In one example, Tateishi et al. (Biochemical and Biophysical Research Communications (2007) 352: 635) show that inhibition of GSK-3 enhances growth and survival of human cardiac stem cells (hCSCs) recovered from the neonatal or adult human heart and having mesenchymal features.
For example, Rulifson et al (PNAS 144, 6247-6252, (2007)) states “Wnt signaling stimulates islet β cell proliferation.
In another example, WO2007016485 reports that addition of GSK-3 inhibitors to the culture of non-embryonic stem cells, including multipotent adult progenitor cells, leads to the maintenance of a pluripotent phenotype during expansion and results in a more robust differentiation response.
In another example, US2006030042 uses a method of inhibiting GSK-3, either by addition of Wnt or a small molecule inhibitor of GSK-3 enzyme activity, to maintain embryonic stem cells without the use of a feeder cell layer.
In another example, WO2006026473 reports the addition of a GSK-3B inhibitor, to stabilize pluripotent cells through transcriptional activation of c-myc and stabilization of c-myc protein.
In another example, WO2006100490 reports the use of a stem cell culture medium containing a GSK-3 inhibitor and a gp130 agonist to maintain a self-renewing population of pluripotent stem cells, including mouse or human embryonic stem cells.
In another example, Sato et al. (Nature Medicine (2004) 10:55-63) show that inhibition of GSK-3 with a specific pharmacological compound can maintain the undifferentiated phenotype of embryonic stem cells and sustain expression of pluripotent state-specific transcription factors such as Oct-3/4, Rex-1, and Nanog.
In another example, Maurer et al (Journal of Proteome Research (2007) 6:1198-1208) show that adult, neuronal stem cells treated with a GSK-3 inhibitor show enhanced neuronal differentiation, specifically by promoting transcription of β-catenin target genes and decreasing apoptosis.
In another example, Gregory et al (Annals of the New York Academy of Sciences (2005) 1049:97-106) report that inhibitors of GSK-3B enhance in vitro osteogenesis.
In another example, Feng et al (Biochemical and Biophysical Research Communications (2004) 324:1333-1339) show that hematopoietic differentiation from embryonic stem cells is associated with down-regulation of the Wnt/β-catenin pathway, where Wnt is a natural inhibitor of GSK3.
Therefore, there still remains a significant need to develop methods for treating pluripotent stem cell such that they can be expanded to address the current clinical needs, while retaining the potential to differentiate into pancreatic endocrine cells, pancreatic hormone expressing cells, or pancreatic hormone secreting cells.